It is well known that the organic light emitting diode (OLED) was initially invented and proposed by the Eastman Kodak Company through a vacuum evaporation method. Tang and VanSlyke of the Kodak Company deposited an electron transport material such as Alq3 on a transparent indium tin oxide (abbreviated as ITO) glass formed with an organic layer of aromatic diamine thereon, and subsequently completed the fabrication of an organic electroluminescent (EL) device after a metal electrode was vapor-deposited onto the Alq3 layer. The organic EL device has become a new generation lighting device or display because of high brightness, fast response speed, light weight, compactness, true color, no difference in viewing angles, the lack of any LCD backlight plates, and low power consumption.
Recently, some interlayers such as an electron transport layer and a hole transport layer have been added between the cathode and the anode to increase the current efficiency and power efficiency of the OLEDs. For example, an OLED 100 shown as FIG. 1 includes a cathode 11, an electron injection layer 12, a light emitting layer 15, a hole transport layer 17, and an anode 18.
In the device function concept, the light emitted by the OLED 100 results from excitons produced by the recombination of electrons and holes in the light emitting layer 14. However, according to theoretical speculation, the ratio of the excitons with a singlet excited state and the excitons with a triplet excited state is 3:1. So, when a small molecular fluorescent material is used as the light-emitting layer 14 of the OLED 100, about 25% of the excitons are used to emit light, and the other 75% of the excitons in the triplet excited state are lost through a non-luminescence mechanism. For this reason, the general fluorescent material performs at a maximum quantum yield of 25%, a limit which amounts to an external quantum efficiency of 5% in the device.
Moreover, researchers further found that certain hole transport type materials can simultaneously perform electron confining, such as materials represented by the following Formulas 1′ and 2′. Formula 1′ represents the chemical structure of tris(4-carbazoyl-9-ylphenyl)amine, which is abbreviated TCTA. Formula 2 represents the chemical structure of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine, abbreviated NPB.

In addition, for effective blue-emitting performance in OLED applications, researchers have developed hole-transporting type, blue-emitters based on triarylamine dimer regimes, such as IDE-102, N-STIF-N developed in my laboratory, and spirobifluorene-based systems. These materials are represented by the following Formulas 3′, 4′, and 5′.

Recently, to effectively increase the light emitting performance of OLEDs, OLED manufactures and researchers have made great efforts to develop electron transport materials with hole blocking functionality, such as TmPyPb, TPBi, 3TPYMB, BmPyPb, and DPyPA represented by following Formula 6′-10′, respectively. TmPyPb is the abbreviation of 3,3′-[5′-[3-(3-Pyridinyl)phenyl][1,1′:3′,1″-terphenyl]-3,3″-diyl]bispyridine, TPBi is the abbreviation of 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene, 3TPYMB is the abbreviation of tris(2,4,6-triMethyl-3-(pyridin-3-yl)phenyl)borane, BmPyPb is the abbreviation of 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene, and DPyPA is the abbreviation of 9,10-bis(3-(pyridin-3-yl)phenyl) anthracene.

In spite of various electron transport materials with hole blocking functionality having been developed, the phosphorescence OLEDs that use these electron transport materials still cannot perform outstanding luminous efficiency with a long device lifetime. Accordingly, because the conventional or commercial electron transport materials with hole blocking functionality still have drawbacks, the inventor of the present application has made great efforts to make inventive research and eventually discovered a series of quinoxaline-fused, spirally configured cis-stilbene/fluorene hybrid materials bearing cyanoaryl and/or cyano-heteroaryl subunits as hole-blocking type electron-transporters and emitters for the OLED.